C++11 styled callbacks? - c++

Question

I have a void function inside of a class. In old C++ i'd make a function static taking the class name as a parameter and had my own class which took a static void function + a void* for me to easily call it.
However that feels old school. It also isn't templated which feels like i could be doing more. What is a more modern way of creating callbacks to myclassVar.voidReturnVoidParamFunc

Answer 1

Use std::function and lambdas (or std::bind()) to store callables:
#include <functional>
#include <iostream>
class Test
{
public:
void blah() { std::cout << "BLAH!" << std::endl; }
};
class Bim
{
public:
void operator()(){ std::cout << "BIM!" << std::endl; }
};
void boum() { std::cout << "BOUM!" << std::endl; }
int main()
{
// store the member function of an object:
Test test;
std::function< void() > callback = std::bind( &Test::blah, test );
callback();
// store a callable object (by copy)
callback = Bim{};
callback();
// store the address of a static function
callback = &boum;
callback();
// store a copy of a lambda (that is a callable object)
callback = [&]{ test.blah(); }; // often clearer -and not more expensive- than std::bind()
callback();
}
Result:
BLAH!
BIM!
BOUM!
BLAH!
Compiles and run: http://ideone.com/T6wVp
std::function can be used as any copyiable object, so feel free to store it somewhere as a callback, like in object's member. It also means that you can freely put it in standard containers, like std::vector< std::function< void () > > .
Also note that equivalent boost::function and boost::bind have been available for years.

Answer 2

For an example of passing in parameters to a C++ 11 callback using Lambda's and a vector, see http://ideone.com/tcBCeO or below:
class Test
{
public:
Test (int testType) : m_testType(testType) {};
void blah() { std::cout << "BLAH! " << m_testType << std::endl; }
void blahWithParmeter(std::string p) { std::cout << "BLAH1! Parameter=" << p << std::endl; }
void blahWithParmeter2(std::string p) { std::cout << "BLAH2! Parameter=" << p << std::endl; }
private:
int m_testType;
};
class Bim
{
public:
void operator()(){ std::cout << "BIM!" << std::endl; }
};
void boum() { std::cout << "BOUM!" << std::endl; }
int main()
{
// store the member function of an object:
Test test(7);
//std::function< void() > callback = std::bind( &Test::blah, test );
std::function< void() > callback = std::bind( &Test::blah, test );
callback();
// store a callable object (by copy)
callback = Bim{};
callback();
// store the address of a static function
callback = &boum;
callback();
// store a copy of a lambda (that is a callable object)
callback = [&]{ test.blah(); }; // might be clearer than calling std::bind()
callback();
// example of callback with parameter using a vector
typedef std::function<void(std::string&)> TstringCallback;
std::vector <TstringCallback> callbackListStringParms;
callbackListStringParms.push_back( [&] (const std::string& tag) { test.blahWithParmeter(tag); });
callbackListStringParms.push_back( [&] (const std::string& tag) { test.blahWithParmeter2(tag); });
std::string parm1 = "parm1";
std::string parm2 = "parm2";
int i = 0;
for (auto cb : callbackListStringParms )
{
++i;
if (i == 1)
cb(parm1);
else
cb(parm2);
}
}